Two independent mol-ecules comprise the asymmetric unit in the title compound, C18H20N2O4. One of the mol-ecules exhibits disorder in one of its 4-piperidone rings, which is disposed over two orientations [site occupancy of the major component = 0.651 (5)]. The first independent mol-ecule and the minor component of the second disordered mol-ecule are virtually superimposable. The central four C atoms in the major component of the disordered mol-ecule have an opposite orientation. All the 4-piperidone rings have a chair conformation. The carbonyl groups in each mol-ecule have approximate anti conformations [O=C⋯C=O = 146.2 (2) and -159.9 (2)°]. The 4-piperidone rings lie to opposite sides of the central benzene ring in both mol-ecules. In the crystal, mol-ecules are linked by C - H⋯O inter-actions. The crystal studied was found to be a non-merohedral twin (twin law -1 0 0, 0 1 0, 0 - 1/2 - 1), the fractional contribution of the minor component being approximately 11%.